U.S. Pat. No. 7,106,310, entitled “Acoustic Wave Touch Actuated Switch” (the “'310 patent”), discloses an acoustic wave switch that includes a substrate with an acoustic wave cavity, or resonator, formed therein such that the mass per unit area of the acoustic cavity is greater than the mass per unit area of the substrate adjacent the acoustic cavity. A transducer is mounted on the acoustic cavity for generating an acoustic wave that is substantially trapped in the cavity. A touch on the touch surface of the acoustic cavity absorbs acoustic wave energy and can produce a detectable change in the impedance of the transducer.
As noted above, the '310 patent discloses a system in which a touch can be detected based on a change in impedance of the transducer. Optionally, a control system can detect a sensed event, such as a touch on an acoustic wave switch/sensor, such as shown and described in the '310 patent, based on the time that it takes for an acoustic wave signal from the transducer to decay to a predetermined level. Such a system and method is described in United States Patent Application Publication No. 2004/0246239, entitled “Acoustic Wave Touch Detection Circuit and Method” (the “'239 application”).
The '310 patent and the '239 application both disclose systems in which a plurality of acoustic wave cavities or resonators are positioned on a substrate. As noted in the '310 patent, the substrate may be formed of metal, plastic, glass, ceramics, etc. that are capable of supporting a resonant acoustic wave.
In order to manufacture an acoustic wave switch, a transducer is bonded to a substrate or panel with an adhesive. A circuit board assembly connects to the transducer.
FIG. 1 illustrates a bottom view of an acoustic wave switch 10. FIG. 2 illustrates a cross-sectional view of the acoustic wave switch 10 through line 2-2 of FIG. 1. Referring to FIGS. 1 and 2, the acoustic wave switch 10 includes a substrate 12 having a mesa 14 defined by an acoustic cavity moat 16. A transducer 18, such as a PZT (Lead Zirconate Titanate) transducer, is secured to the substrate 12 through an adhesive 20. In particular, the transducer 18 is adhesively bonded to a surface of an acoustic wave cavity 22.
In order to manufacture a functional acoustic wave switch 10, care is taken to use an appropriate adhesive 20, such as an acoustically transmissive epoxy, and ensure a proper bondline thickness. For example, adhesives 20 with particular acoustic properties are used in order to ensure that the transducer 18 is able to resonate the acoustic wave cavity 22. Further, an overly thick bondline may dampen or impede resonance within the acoustic wave cavity 22. In general, a thin, rigid bond is effective in transferring energy from the transducer 18 to the acoustic wave cavity 22 with minimal energy loss. Various types of epoxies, such as those manufactured and sold by Bondline Electronic Adhesives of Sunnyvale, Calif., may be used.
In general, various types of adhesives may be used to produce a functional acoustic wave system. For example, epoxies, cyanoacrylates and methacrylates may be used to bond the transducer 18 to the substrate 12. Epoxies are particularly well-suited due to the strength and reliability of the subsequent bond.
Epoxies typically require, however, several minutes, or even hours, to cure. As such, the manufacturing process may be long and costly. During the manufacturing process, the transducer 18 is forced into or onto the substrate 12 (i.e., pressure is applied to the transducer 18 in order to force it onto or into the substrate 12) in order to minimize the bond thickness (thereby increasing the efficiency of the acoustic wave transfer). Typically, heat is applied to the system during assembly for at least one hour in order to cure the adhesive 20.
Customized clamping jigs and fixtures are typically used during the manufacturing process. Clamps and fixtures are used to secure the transducer 18 to the substrate 12 during the curing process so that the transducer 18 does not shift with respect to the substrate 12. The clamping jigs and fixtures are placed in a curing oven with the product and must withstand the temperature and abuse of the curing process. Thus, the clamping jigs and fixtures are typically expensive components. Moreover, the clamping jigs and fixtures take up considerable oven space, are typically specific to a given product and are not readily adaptable for use with respect to other products.
Consequently, the capital, equipment and manpower used to manufacture acoustic wave switches are relatively high. Thus, a particular manufacturer may find the costs, labor and time associated with such a manufacturing process to be prohibitively high.